CONTINUOUS RENAL REPLACEMENT THERAPY Joshua H. Wolf, MD Transplant Nephrologist Piedmont Transplant Institute

Renal Replacement Therapy (RRT) Indications = A E I O U Acidosis Electrolytes (hyperkalemia, hyponatremia) Intoxication (methylene glycol) Overload – Volume Overload Uremia

Continuous Renal Replacement Therapy (CRRT) A E I O U in the setting of: Hypotension Oligoanuria and receiving multiple blood products Pre-liver patient who is actively bleeding requiring multiple blood products Hyponatremia refractory to medical intervention Critically ill, intubated with drug intoxication and tenous volume status Pre-liver patient who needs aggressive volume removal to optimize for liver transplant

Continuous Renal Replacement Therapy (CRRT) SCUF- Slow Continuous Ultrafiltration Ultrafiltration CVVH- Continuous Veno-Venous Hemofiltration Convection CVVHD- Continuous Veno-Venous Hemodialysis Diffusion CVVHDF- Continuous Veno-Venous Hemodiafiltration Diffusion and Convection

SCUF-Ultrafiltration Slow continuous ultrafiltration: Requires a blood and an effluent pump. No dialysate or replacement solution. Fluid removal up to 2 liters/hr can be achieved. Primary Goal Safe management of fluid removal Large fluid removal via ultrafiltration SCUF (slow continuous ultrafiltration) when using this therapy, significant amounts of fluid are removed from the patient. No dialysate or replacement fluid is used because solute control is not a goal of this therapy. Ultrafiltration can be adjusted to cause dramatic fluid shifts. SCUF treatment utilize UFR’s of up to 2L/hr in some cases. The only pumps needed for this therapy is a blood pump and an effluent pump.

Transport mechanism: Ultrafiltration Movement of fluid through a semi-permeable membrane driven by a pressure gradient (hydrostatic pressure). The effluent pump forces plasma water and solutes across the membrane in the filter. This transport mechanism is used in SCUF, CVVH, CVVHD, and CVVHDF. Ultrafiltration is defined as…. Read the slide. The pressure gradient in the extracorporeal circuit is created by positive, negative, or oncotic pressure from non-permeable solutes. For our purposes, ultrafiltration results in removal of fluid (plasma water) from the patient’s blood. The fluid that is removed is sometimes referred to as “Ultrafiltrate or UF”.

SCUF Return Pressure Air Detector Patient Syringe pump Blood Pump Return Clamp Hemofilter Filter Pressure Access Pressure Effluent Pressure Effluent Pump Pre Blood Pump This slide depicts the SCUF (slow continuous ultrafiltration) is a therapy that uses no dialysate or replacement solution.On the right hand side of the screen you see a Pre-blood pump that could deliver anticoagulation solution at the patient access. The there is really only 2 pumps that are required for this therapy: Blood pump, Effluent pump, and if desired the Pre-blood pump. Plasma water is removed by ultrafiltration.

CVVHD-Diffusion Continuous veno-venous hemodialysis Requires the use of blood, effluent and dialysis pumps. Replacement solution is not required. Plasma water and solutes are removed by diffusion and ultrafiltration. CVVHD (continuous veno-venous hemodialysis) is a therapy that uses dialysate solution on the fluid side of the filter to increase solute exchange by diffusion. Replacement solution is not required for this therapy. The pumps required for this therapy are as follows: Blood, dialysate and effluent pump. Plasma water and solutes are removed by diffusion and ultrafiltration.

Transport Mechanisms: Diffusion Removal of small molecules by diffusion through the addition of dialysate to the fluid side of the filter. Dialysate is used to create a concentration gradient across a semi permeable membrane Dialysis uses a semi permeable membrane for selected diffusion This transport mechanism is used in: CVVHD CVVHDF Diffusion is another transport mechanism and is defined as…. Read first bullet on slide. Dialytic therapies use a semi permeable membrane (the filter) through which solutes diffuse selectively, based on particle size, as blood passes through the filter. Solutes are defined as any substance that dissolves in a liquid to form a solution. Solutes removed by diffusion during CRRT might be waste products, electrolytes, buffers, etc.

Dialysate Solutions Through diffusion, dialysate corrects underlying metabolic problems Dialysate is dependent on buffering agent, electrolytes, and glucose Dialysate formulas should reflect normal plasma values to achieve homeostasis The physician will also prescribe the dialysate composition as well as the delivery flowrates. Dialysate solution usually reflect normal plasma values. Through diffusion dialysate solution corrects underlying metabolic problems.

Dialysate

CVVHD Return Pressure Air Detector Return Clamp Syringe Pump Blood Pump Patient Hemofilter Filter Pressure Access Pressure Effluent Pressure BLD Dialysate Pump Pre Blood Pump Effluent Pump This schematic depicts a CVVHD flowpath. Describe the blood flowpath through the hemofilter and back to the patient. Then show green dialysate entry into the hemofilter (counter-current flow) and effluent removal through the yellow line/bag. Prismaflex allows use of the Pre blood pump fluid/anticoagulant infusion. The white bag on the right-hand side of the slide can deliver anticoagulation solution. We really want to focus on the green bag on the left hand side of the slide. This is the dialysate solution that is going to be delivered to the fluid side of the filter. The dialysate solution enters at the top of the filter and travels counter-current of the blood. The counter-current flow increases solute removal. 306100135

The patients blood contains a high concentration of unwanted solutes that can be effectively removed by diffusion. Diffusions key mechanism is to move a solute from a higher concentration gradient to a lower concentration gradient. For example, let us assume the blood in the filter has a high concentration of potassium molecules and on the fluid/dialysate compartment has a low concentration of potassium. The potassium gradually diffuses through the membrane from the area of a higher potassium concentration to the area of a lower potassium concentration until it is evenly distributed.

CVVHDF Continuous veno-venous hemodiafiltration Requires the use of a blood, effluent, dialysate and replacement pumps. Both dialysate and replacement solutions are used. Plasma water and solutes are removed by diffusion, convection and ultrafiltration. CVVHDF (continuous veno-venous hemodiafiltration) combines the benefits of CVVH and CVVHD using both convective and diffusive transport mechanisms. Replacement and dialysate fluids are both employed. The pumps required for this therapy are as follows: A blood, dialysate, replacement and effluent pumps.

Transport Mechanisms: Diffusion and Convection Removal of small molecules by diffusion through the addition of dialysate solution. Removal of middle to large molecules by convection through the addition of replacement solution. This transport mechanism is used in: CVVHDF The use of both diffusion and convection transport mechanism create a therapy called hemodiafiltration. This specific therapy combines dialysate solution to create diffusive clearance of small molecules, and replacement solution to create convective clearance of middle to large molecules.

Intratherapy Monitoring The critical care nurse must continuously monitor the following parameters during CRRT Blood flow rate Ultrafiltration flow rate Dialysate/replacement flow rate Alarms and responses Color of ultrafiltrate/filter blood leak Color of CRRT circuit Blood pressure Patency of circuit Hemodynamic stability Level of consciousness Acid/base balance Electrolyte balance Hematological status Infection Nutritional status Air embolus It is imperative that CRRT is continuously monitor for the following parameters: Blood pressure, Patency of circuit,Hemodynamic stability,Level of consciousness, Acid/base balance, Electrolyte balance, Hematological status, Infection,Nutritional status, Air embolus, Blood flow rate, Ultrafiltration flow rate, Dialysate/replacement flow rate, Alarms and responses, Color of ultrafiltrate/filter blood leak, Color of CRRT circuit.

Real time CRRT Monitoring

Citrate

So what is Citrate Toxicity? Liver converts Citrate  Bicarbonate Liver stops working: Citrate accumulates Worsening AG metabolic acidosis  Dissociation of Calcium and Citrate = Elevated serum calcium level Binds up iCa = decreases iCa in the blood

How do you manage a patient with worsening acidosis on CRRT? Step 1: Increase bicarbonate in dialysate Standard is 22 mEq/L  can increase to 32 mEq/L Step 2: Can evaluate for citrate toxicity Discontinue citrate if needed Step 3: Replacement fluid default is NS @ 200 cc/hr Consider changing to Free water with 150 meQ/L of NaHCO3

Questions?